The use of reactance elements, such reactors or capacitors or a combination thereof, for phase compensation in AC networks is known. It is also known to connect such reactance elements to the network with thyristors so that the compensation can be made variable, either in steps, by dividing the reactance elements into smaller groups where each group constitutes its own compensating stage with its won thyristor connection, or continuously by phase angle control of the thyristors. In the latter case control may give rise to harmonics in the AC network if the control is not properly arranged.
One advantage of thyristors is their effective control. On the other hand, thyristors as a rule demand a certain amount of service or maintenance which requires disconnecting them from the network. Disconnection of the thyristors results in disconnection of the reactance elements which is not desirable. The same is true, to an evan higher degree, in the case of disconnection for reasons of protection.
It is therefore one object of the invention to provide phase compensation for AC networks with a reactance element and thyristor control which allows the thyristors to be disconnected and which leaves the reactance in the circuit.